Nonvolatile semiconductor storage devices such as a nonvolatile semiconductor memory typically have a contact region located between select gate electrodes which are used for selection of cell strings. In the contact region, an impurity diffusion layer is formed in order to reduce contact resistance. A contact is typically formed in an active layer also referred to as an element region which is formed by delineating a semiconductor substrate with element isolation trenches.
The doped impurities may, however, strain the semiconductor substrate and cause swelling of the element region hosting the diffusion layer. This may destroy the crystal structure of the semiconductor substrate and cause crystal defects. The crystal defects may lead to shorting of the cell strings which may cause performance degradations such as an increase in junction leakage current.